This invention is generally directed to imaging members, and electrostatographic imaging and printing processes thereof. More specifically, the present invention is directed to layered imaging members wherein there is selected, especially for the photogenerating pigments, a block copolymer dispersant. In one embodiment of the present invention, there are provided layered photoconductive imaging members with excellent xerographic properties, inclusive of high charge acceptance, low dark decay, high photosensitivity in the wavelength regions of from about 400 to about 800 nanometers, enabling their selection for electrophotographic, especially xerographic, imaging systems and printers. In one embodiment of the invention of the present application, there are provided imaging members with photoconductive layers comprised of known photogenerating pigments dispersed in block copolymers, such as A-B block copolymers, like polystyrene/vinylpyridine block copolymers, and charge or hole transport layers, especially those comprised of aryl amines, which members are sensitive to light in the wavelength region of from about 400 to about 820 nanometers, depending on the photogenerating pigment selected. The resulting members can thus be responsive to illumination of, for example, from about 660 to about 720 nanometers originating from laser diodes printing apparatuses. The photoresponsive imaging members of the present invention can, for example, contain situated between the supporting substrate and the charge transporting layer, a photogenerating layer.
The photogenerating layer can be comprised of a photosensitive pigment, such as benzimidazole perylene (BZP), reference U.S. Pat. No. 4,587,189, the disclosure of which is totally incorporated herein by reference, in a resinous binder. To effectively permit coating of the photogenerating layer or binder generator layer (BGL) on the supporting substrate, it is usually necessary to dissolve the polymeric binder in a solvent suitable for coating, and disperse the photogenerator pigment in the solvent/binder mixture. Submicron size pigment particles are desired which often requires extensive grinding of the mixture in a ball mill or attritor. Large pigment particles due to inefficient grinding or reflocculation are undesirable since they result in coating defects which subsequently surface as print defects. Therefore, it is of importance that the dispersion once formed remain stable for a minimum of about seven to about 14 days to allow completion of the coating. For example, dip coating would require the dispersion to remain stable for a period of months, for example up to seven months. When BZP is dispersed in commercially available binder resins, such as polycarbonates, polyesters, and polyvinylcarbazoles, some settling or flocculation is evident within about 24 hours.
The addition of certain A-B diblock copolymers to a pigment, prior to milling, can provide superior dispersion, reference H. L. Jakubauskas, Journal of Coatings Tech., Vol. 58, No. 736, pages 71 to 82, 1986. The A block acts as an anchor on the pigment surface, while the B block extends out from the surface to pro vide steric stabilization. However, these types of materials cannot usually be incorporated into the binder generator layer (BGL) without adversely affecting the sensitivity, dark decay and cyclic stability of the resulting photoreceptor device. The block copolymer dispersants of this invention enable improved imaging member sensitivity, and excellent dark decay when compared to control devices, or imaging members with a MAKROLON.RTM. polycarbonate binder, or the specific aforementioned diblocks of the prior art. In addition, with the block copolymers of the present invention, the excellent cyclic stability characteristic of, for example, a BZP photoreceptor was not compromised.
Advantages achievable with the imaging members of the present invention include excellent photogenerating pigment dispersion, stable dispersion in the block copolymer, design of the A-B block copolymer wherein the length and composition of the A segment enables it to bind or anchor firmly to the photogenerating pigment surface, while the B segment functions as a steric stabilizer to prevent reflocculation of the photogenerating pigment after dispersion. More specifically, BZP dispersions produced with the A-B block copolymers of this invention are stable in excess of one year, for example about 1.5 years, in embodiments and enable photogenerator layer coatings with substantially reduced defect levels when compared to the binders indicated here. In addition, these block copolymers function both as the dispersant and the binder. Alternatively, they can be used in combination with a compatible binder resin if desired.
Certain layered imaging members are known, including those comprised of separate generating layers, and transport layers as described in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference; and overcoated photoresponsive materials containing a hole injecting layer overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer; and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain aryl diamines as mentioned therein.
The following United States patents are mentioned: U.S. Pat. No. 4,299,896 which discloses imaging members with a photosensitive layer selected from the disazo pigments of the formulas illustrated, for example, in the Abstract, and in column 2; U.S. Pat. No. 4,314,015 wherein the disazo pigments for the imaging member are of the formula as illustrated in the Abstract, for example, and column 2; U.S. Pat. No. 4,666,810 wherein the azo pigments are illustrated in column 2 for example; and U.S. Pat. No. 4,797,337 wherein the disazo photogenerating pigment is of the formula as illustrated in the Abstract, for example, which disazos may contain a SO.sub.2 group.
The use of selected perylene pigments as photoconductive substances is also known. There is thus described in Hoechst European Patent Publication 0040402, DE3019326, filed May 21, 1980, the use of N,N'-disubstituted perylene-3,4,9,10-tetracarboxyldiimide pigments as photoconductive substances. Specifically, there is, for example, disclosed in this publication N,N'-bis(3-methoxypropyl)perylene-3,4,9,10-tetracarboxyldiimide dual layered negatively charged photoreceptors with improved spectral response in the wavelength region of 400 to 700 nanometers. A similar disclosure is revealed in Ernst Gunther Schlosser, Journal of Applied Photographic Engineering, Vol. 4, No. 3, page 118 (1978). There are also disclosed in U.S. Pat. No. 3,871,882 photoconductive substances comprised of specific perylene-3,4,9,10-tetracarboxylic acid derivative dyestuffs. In accordance with the teachings of this patent, the photoconductive layer is preferably formed by vapor depositing the dyestuff in a vacuum. Also, there are specifically disclosed in this patent dual layer photoreceptors with perylene-3,4,9,10-tetracarboxylic acid diimide derivatives, which have spectral response in the wavelength region of from 400 to 600 nanometers. In U.S. Pat. No. 4,587,189, the disclosure of which is totally incorporated herein by reference, there is illustrated a layered imaging member with a bis perylene pigment photogenerating component.
Additional references illustrating layered organic electrophotographic photoconductor elements with azo, bisazo, and related compounds include U.S. Pat. No. 4,390,611, U.S. Pat. No. 4,551,404, U.S. Pat. No. 4,596,754, Japanese Patent 60-64354, U.S. Pat. Nos. 4,400,455, 4,390,608, 4,327,168, 4,299,896, 4,314,015, 4,486,522, 4,486,519, 4,555,667, 4,440,845, 4,486,800, 4,309,611, 4,418,133, 4,293,628, 4,427,753, 4,495,264, 4,359,513, 3,898,084, 4,830,944, 4,820,602, and Japanese Patent Publication 60-111247.
U.S. Pat. No. 4,755,443 discloses a photoreceptor for electrophotography which comprises a charge carrier generating material and charge transport material wherein one charge generating material is a metal phthalocyanine or a metal-free phthalocyanine. The layer containing the generator material also contains an organic amine. Other carrier generating substances can be used in combination with the phthalocyanine generator material, including azo pigments, anthraquinone dyes, perylene dyes, polycyclic quinone dyes, and methine stearate pigments.
Illustrated in copending patent application U.S. Serial No. 084,106 filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, is a process for the preparation of a photogenerating composition which comprises mixing titanyl phthalocyanine Type IV with an AB block copolymer, such as polystyrene-4-vinyl pyridine in a suitable solvent.
U.S. Pat. No. 4,424,266 discloses an electrophotographic photosensitive element having a conductive support and a photosensitive layer comprising a carrier generating phase layer containing a carrier generating material selected from the group consisting of perylene dyes, polycyclic quinones, and azo dyes, and a carrier transporting phase layer containing a hydrazone carrier transporting material. The carrier generator materials can be used either singly or in combination.
U.S. Pat. No. 4,882,254, the disclosure of which is totally incorporated herein by reference, discloses a layered photoresponsive imaging member which comprises a supporting substrate, a photogenerator layer comprising a mixture of first and second pigments, and an aryl amine hole transport layer. The mixture of pigments is selected from perylenes and phthalocyanines, polycyclic quinones and phthalocyanines, or perinones and phthalocyanines.
Photoresponsive imaging members containing perinone and perylene compounds are also known. For example, European Patent Publication 0040402, DE3019326, filed May 21, 1980, discloses the use of N,N'-disubstituted perylene-3,4,9,10-tetracarboxyldiimide pigments as photoconductive substances.
Imaging members with phthalocyanine materials are also known as disclosed in, for example, U.S. Pat. Nos 3,594,163, 3,657,272, 3,816,118, 3,862,127, 3,903,107, 3,927,026, 3,932,180, 3,932,454, 4,031,109, 4,098,795, and U.S. Pat. No. Re. 27,117, the disclosures of each of which are totally incorporated herein by reference.